Spark plug having an auxiliary series spark gap in parallel with the main spark gap



G. H. BARRY G HAVING AN AUXILIARY SERIES SPARK GAP Nov. 14, 1967 SPARK PLU IN PARALLEL WITH THE MAIN SPARK GAP Filed July 15 1964 i T m2 Q INVENTOR. GEOPGEH. BARRY PATENT AGNT United States Patent M 3,353,052 SPARK PLUG HAVING AN AUXILIARY SERIES SPARK GAP IN PARALLEL WITH THE MAIN SPARK GAP George H. Barry, 1044 Mofiett Circle, Palo Alto, Calif. 94303 Filed July 15, 1964, Ser. No. 382,702 7 Claims. (Cl. 313-123) The present invention relates generally to ignition systems, and more particularly, to a multi-gap spark generation arrangement for internal combustion engines or the like.

It has long been recognized that a wide spark-plug gap is desirable in spark ignition of internal combustion engines. A longer spark provides more reliable ignition, especially under conditions of idling or part throttle operation, when the relatively ratified charge is more difficult to ignite than the dense, full throttle charge. Three reasons have been advanced for the improved performance of wide gaps; First, a large volume of gas is heated by the spark; second, under conditions of imperfect carburetion the longer spark path is more likely to contain a combustible mixture; and third, the mixture in the immediately vicinity of the spark is less quenched by heat loss to the adjacent walls with a wider gap. The trend over the past thirty years toward wider plug gaps in automotive engines reflects the importance of this factor in the light-load engine efliciency, especially when it is realized that gaps have been increased despite the increase in compression ratio, which, in itself, places greater demands on the ignition system.

The upper limit on plug gap length is imposed at full throttle, when the available ignition voltage must be capable of forming an are through the high-density charge. It may be observed that, under these conditions, a short spark gap is much less a liability than at part throttle; the full throttle charge is much more combustible as a result of its higher density and the fact that it is common practice to carburet for exceedingly rich full throttle mixtures.

Accordingly, it follows that a relatively long gap length is preferable under idling conditions while a relatively short gap is preferable at full throttle conditions, and it is a general object of the present invention to provide a spark generation arrangement employing a plurality of spark gaps of differing lengths and individually operable under diverse conditions of engine operation to optimize such operation.

More particularly, it is a feature of the invention to provide a spark generation arrangement for internal combustion engines or the like which automatically provides for firing across a relatively long gap at idling or part throttle conditions and across a relatively short gap as full throttle conditions are approached.

Specifically, it is a feature of the invention to provide a spark generation arrangement for internal combustion engines utilizing a novel arrangement including an auxiliary gap for controlling a selection of which of a plurality of spark gaps of variant dimensions is rendered effective to instigate ignition.

It is a related feature of the invention to provide in a spark generation arrangement means for controlling which of a plurality of spark gaps is fired automatically in response to the density of the combustible mixture.

Yet another feature of the invention is the provision of a spark generation arrangement including an auxiliary gap arranged in series electrical connection with a spark gap in a manner which assures sequential firing of the two gaps.

Additionally, it is a feature of the invention to provide a spark generation arrangement for internal combustion Patented Nov. 14, 1967 engines or the like wherein a plurality of spark gaps are located in adjacent relationship in the combustion chamber of the engine.

A related feature of the invention is the provision of a plurality of adjacent spark gaps wherein one electrode adapted for connection to ground forms a terminal for all of the gaps of variant dimensions wherefore adjustment of the position of such grounded electrode either increases or decreases all gap lengths simultaneously.

These as well as other objects and features of the invention will become more apparent from a perusal of the following description taken in conjunction with the accompanying drawing wherein:

FIG. 1 is a longitudinal central sectional view taken through a spark plug constituting an exemplary embodiment of the present invention, and

FIG. 2 is a circuit diagram explanatory of the operation of the spark plug shown in FIG. 1.

Generally, a spark generation arrangement for internal combustion engines or the like in accordance with the present invention includes means forming two or more separate spark gaps of differing dimensions together with means for selectively applying an ignition potential to one or another of said gaps in accordance with existent engine operating conditions.

The arrangement can be embodied in a simple dual gap spark plug, as shown in FIG. 1, whose overall dimensions and configuration are such that the spark plug can be utilized as a replacement for a conventional plug in existent internal combustion engines. Briefly, the spark plug includes an outer, generally cylindrical hollow metallic casing 10 which is exteriorly threaded adjacent its lower end for screwed attachment into the interiorly threaded socket for existent plugs. It will be understood that such threaded connection establishes an electrical ground connection to the exterior metallic casing of the plug.

rorn the lower extremity of the metallic casing 10, an inwardly and downwardly extending metallic tip projects to form a grounded electrode 12 providing one terminal for each of two spark gaps 14, 16 whose other terminals are formed by the lower extremities of two electrodes 18, 20 in the form of elongated cylindrical rods extending centrally through the metallic casing 10 and held in insulated relationship from it and from each other by a suitable ceramic insulator 22 attached to the casing by a conventional sealing compound indicated at 24.

In view of the inclined configuration of the grounded electrode 12, the lengths of the two spark gaps 14, 16 are different. Typically, for operation of existent internal combustion engines, the shorter gap 14 illustrated at the right in FIG. 1 has a length of approximately 0.020 inch while the longer gap 16 on the left has a length of 0.070 inch. It is to be specifically observed that both gaps lin in the combustion chamber of the engine, or more particularly, in one particular cylinder thereof; and it will also be observed that movement of the grounded electrode 12 effects either an increase or decrease in both spark gap lengths. Accordingly, simultaneous adjustment of the plug for any particular engine requirements can readily be made.

The longer spark gap 16 can be considered as the con ventional spark gap such as found on standard spark plugs and, as a consequence, the elongated electrode 18 is connected at its upper end directly to a metallic cap 26 to which the ignition wire from the ignition coil (not shown) of the engine can be connected in a conventional fashion. On the other hand, the electrode 20 which forms the shorter gap 14 is foreshortened so as to be spaced from the metallic cap 26 of the plug to form an auxiliary gap 28 whose typical length will be 0.200 inch, and, as will be obvious, is located outside of the engine combustion chamber.

When a spark plug, as illustrated in FIG. 1 and as described hereinabove, is placed in operative position in an internalcombustion engine, when the engine is started, the ignition potentialwill be periodically applied to the cap and thus directly to the electrode .18 on the left in FIG. 1 which in conjunction with the grounded electrode 12 provides the long spark gap 16. Under idling or part throttle conditions, the density of the fuel-air mixture in the engine cylinder is relatively low, and upon attainment of full ignition potential, a spark will jump across the long gap 16 to initiate combustion. At increased throttle conditions, the voltage necessary for breakdown increases and before the requisite potential is achieved, firing of the auxiliary gap 28 will occur so that the full ignition potential will be applied across the short spark gap 14 which will, in turn, fire. Since the cornbustible mixture is now richer, the relatively short spark will be adequate to achieve complete combustion. Preferably, as described, the firing of the auxiliary gap 28 and the short ignition gap 14 in series therewith is sequential so that the entire ignition potential is applied across the short' gap 14 and is not divided between the two.

The described operation can be more fully understood by reference to the circuit diagram of FIG. 2 wherein the ignition potential is applied across a capacitor shown in dotted line at 30 and representing thestray capacity present in the ignition coil, distributor, plug wires and long gap 16 of the spark plug. Such full ignition potential is supplied directly across the long gap 15 whose resistance to firing, as explained hereinabove, is relatively low when idling or part throttle conditions are experienced. Such ignition potential is not directly applied to the short gap 14 but rather is initially applied to the auxiliary gap 28 across which capacity, indicated in dotted lines at 32, exists. In addition, leakage resistance exists across the short gap 14, as indicated by the dotted line resistor 34, and this resistance in combination with the capacitance across the auxiliary gap 28 forms an RC circuit. By a controlled choice of the values of the capacitor 32 and resistor 34, the time constant of this RC circuit can be determined so that the auxiliary gap 28 and the short gap 14 will break down in sequence, as mentioned hereinabove. More particularly, if the time constant of this RC circuit is substantially less than the rise time of the ignition potential, the short spark gap 14 will remain sub stantially at zero potential until the auxiliary gap 28has fired, whereupon substantially the entire ignition potential will be applied across the short gap 14 to instigate firing of the latter. Typically,the capacity existing across the auxiliary gap is 2 or 3 picofarads and by control of the leakage resistance through appropriate choice of ceramic material and thickness, the resistance value can be maintained below megohms. Accordingly,.the time constant of the RC circuit will be no more than 20 or 30 microseconds which is considerablye shorter than the 70 to 100 microsecond rise time of typical ignition systems. The desired sequential breakdown of the auxiliary gap 28 and the short gap 14 is accordingly assured,

4 It will be obvious that more gaps than the two described can be incorporated into a spark plug .or other ignition arrangement; and the foregoing description of one simplified embodiment of the invention is presented purely for exemplary purposes and is not to be construed in a limited, sense. The actual scope of the invention is to be indicated only by reference to the appended claims.

What is claimed is:

1. A spark plug which comprises a first electrode adapted for connection to ground, a second electrode adapted for connection to an ignition coil and spaced a predetermined distance from said first electrode to form a first firing gap,'a third electrode spaced from said first electrode a lesser distance than said second electrode to form a second shorter firing gap, and means including an auxiliary gap for electrically connecting said third electrode to said second electrode.

2. A spark generation arrangement for internal combustion engines or the like which comprises a plurality of electrodes arranged to provide a plurality of separate ignition spark gaps of differing dimensions, and means including an auxiliary gap between two of said electrodes for automatically firing across a gap of shorter dimensions upon attainment of a predetermined combustible mixture in the vicinity of said spark gaps.

3. A spark generation arrangement according to claim 2 wherein all of said ignition spark gaps are adjacent one another.

4. A spark generation arrangement according to claim 2 the longer of said gaps, and means including an auxiliary gap for applying the ignition potential to the shorter of said gaps.

6. A spark ignition arrangement according to claim 5 wherein said auxiliary gap is connected to said shorter ignition gap so that a sequential firing of said gaps occurs.

7. A spark ignition arrangement according to claim 6 wherein the time constant determined by the leakage resistance and capacitance across said auxiliary gap is short compared to the rise time of the applied ignition potential.

References Cited UNITED STATES PATENTS 1,131,115 3/1915 Carpentier 313-440 X 1,268,049 5/1918 OGorrnan 313 X- 1,356,349 10/1920 Fitz 3 l3140 X 2,487,319 11/ 1949 Ellis 313-140 X JAMES W. LAWRENCE, Primary Examiner.

C. R. CAMPBELL, Assistant Examiner, 

1. A SPARK PLUG WHICH COMPRISES A FIRST ELECTRODE ADAPTED FOR CONNECTION TO GROUND, A SECOND ELECTRODE ADAPTED FOR CONNECTION TO AN IGNITION COIL AND SPACED A PREDETERMINED DISTANCE FROM SAID FIRST ELECTRODE TO FORM A FIRST FIRING GAP, A THIRD ELECTRODE SPACED FROM SAID FIRST ELECTRODE A LESSER DISTANCE THAN SAID SECOND ELECTRODE TO FORM A SECOND SHORTER FIRING GAP, AND MEANS INCLUDING AN AUXILIARY GAP FOR ELECTRICALLY CONNECTING SAID THIRD ELECTRODE TO SAID SECOND ELECTRODE. 